(1) Field of the Invention
This invention relates to radiographic apparatus of the non-CT (Computed Tomography) type used in medical, industrial and other fields for producing sectional images of patients or objects under examination. More particularly, the invention relates to a technique for generating a three-dimensional sectional image of a region of interest of an object quickly.
(2) Description of the Related Art
Conventional radiographic apparatus include an X-ray radiographic apparatus, for example. The X-ray radiographic apparatus has an X-ray tube and an image intensifier opposed to each other across an object under examination. The X-ray tube is linearly moved in a first direction, and in synchronism therewith the image intensifier is moved in a second direction counter to the first direction. With this movement, the apparatus intermittently performs radiography while varying an angle of X-ray emission from the X-ray tube to the object, such that a given point in a particular sectional plane of the object always corresponds to the same location on the detecting plane of the image intensifier. Then, a process is carried out simply to add detection signals so as to overlap a plurality of projected images acquired by radiography done from varied angles. In this way, the apparatus derives image information on a particular section of the object and image information on adjacent sections at opposite sides of the particular section.
Thus, the above X-ray radiographic apparatus is based on the non-CT type radiographic technique distinct from the X-ray CT type radiographic technique which has made remarkable progress in recent years. That is, the X-ray CT type radiographic technique acquires transmitted images by driving an X-ray tube and an image intensifier opposed to each other across an object under examination to make one revolution (at least a half revolution) about the body axis of the object. An image reconstruction is carried out based on transmitted images acquired while one revolution (at least a half revolution) about the body axis of the object, to produce a sectional image seen in a direction along the body axis of the object. The non-CT type radiographic technique, as does the foregoing X-ray radiographic apparatus, produces a sectional image seen in a direction along the body axis of the object, without causing the X-ray tube and image intensifier to make a half or more revolution about the body axis of the object.
However, the conventional technique noted above has the following drawback. The non-CT type radiographic apparatus cannot generate a three-dimensional sectional image of a region of interest of an object quickly.
Specifically, the conventional non-CT type radiographic apparatus can acquire, in one radiographic operation, only two-dimensional sectional images of a region of interest of an object, including only information on a particular sectional plane and adjacent sectional planes at opposite sides of the particular sectional plane in the region of interest. When it is desired to generate three-dimensional volume data (i.e. a three-dimensional sectional image) of the region of interest, the radiographic operation must be repeated a plurality of times to generate a three-dimensional sectional image by combining two-dimensional sectional images acquired by the repeated radiographic operation. This results not only in the object being exposed an increased number of times, and thus an increased burden, but the generation of a three-dimensional volume data being an extremely time-consuming process.
When, for example, it is desired to obtain a slant sectional image of a region of interest not parallel to the detecting plane of the image intensifier, the radiographic operation must, again, be repeated a plurality of times to generate a three-dimensional sectional image by combining two-dimensional sectional images acquired by the repeated radiographic operation. A desired slant image is computed from the three-dimensional sectional image. Thus, the above drawbacks arise here also.
This invention has been made having regard to the state of the art noted above, and its object is to provide a radiographic apparatus capable of generating a three-dimensional sectional image of a region of interest of an object quickly.
The above object is fulfilled, according to this invention, by a radiographic apparatus for obtaining images of sectional planes in a region of interest of an object under examination by an image reconstruction using projection data acquired by radiographing the object from varied scan positions, the apparatus comprising:
a radiation source for irradiating the object with penetrating electromagnetic waves;
an area detector opposed to the radiation source across the object for detecting electromagnetic waves transmitted through the object;
a scanning device for synchronously moving the radiation source and the area detector for scanning action; and
a back projection unit for performing an image reconstruction to generate three-dimensional volume data of the region of interest by projecting projection data detected in the varied scan positions back to predetermined lattice points of a three-dimensional lattice virtually set to the region of interest of the object radiographed.
With the apparatus according to this invention, the back projection unit performs an image reconstruction to generate three-dimensional volume data of the region of interest by projecting projection data detected in the varied scan positions back to predetermined lattice points of a three-dimensional lattice virtually set to the region of interest of the object radiographed. The apparatus does not use the conventional method in which two-dimensional sectional image data is generated by adding detection signals to superimpose, on a single plane, a plurality of projection images acquired by radiography from varied angles (i.e. projection images acquired from varied scan positions). Instead, an image reconstruction is carried out to generate three-dimensional volume data of the region of interest by projecting projection images acquired from varied scan positions back to predetermined lattice points of the three-dimensional lattice. Three-dimensional volume data of the region of interest may be generated without performing radiography a plurality of times. Thus, three-dimensional volume data of the region of interest of the object is generated quickly.
Preferably, the apparatus further comprises a filtering unit for performing an |xcfx89| filtering process on the projection data detected in the varied scan positions, and outputting the projection data to the back projection unit. This filter application effectively reduces artifacts caused by DC components being emphasized in three-dimensional volume data subsequently generated by the back projection unit.
Preferably, the area detector is a flat panel detector or an image intensifier, which enables a prompt generation of a three-dimensional image of the region of interest of the object.
Preferably, one of the radiation source and the area detector is movable linearly in a first direction, and the other movable linearly in synchronism therewith in a second direction parallel and counter to the first direction. Thus, radiography is carried out for an image reconstruction to generate three-dimensional volume data of the region of interest of the object by moving the radiation source and area detector linearly and parallel to each other with the object in between.
Preferably, the radiation source is revolved in one of parallel planes opposed to each other across the object, and the area detector is revolved in synchronism therewith in the other parallel plane in a direction counter to a direction of revolution of the radiation source. Thus, radiography is carried out for an image reconstruction to generate three-dimensional volume data of the region of interest of the object by individually revolving the radiation source and area detector in the parallel planes with the object in between.
It is also preferred that two arcuate tracks are set on a circumferential track around the object to be opposed to each other across the object, the radiation source is moved along one of the arcuate tracks, and the area detector in synchronism therewith along the other arcuate track to maintain a fixed distance from the radiation source. Thus, radiography is carried out for an image reconstruction to generate three-dimensional volume data of the region of interest of the object by individually moving the radiation source and area detector along the arcuate tracks opposed to each other across the object.
In another aspect of the invention, a radiographic apparatus is provided for obtaining images of sectional planes in a region of interest of an object under examination by an image reconstruction using projection data acquired by radiographing the object from varied scan positions, the apparatus comprising:
a radiation source for irradiating the object with penetrating electromagnetic waves in form of a divergent beam;
an area detector opposed to the radiation source across the object for detecting electromagnetic waves transmitted through the object;
a scanning device for setting two non-orbital tracks opposed to each other across the object, moving the radiation source along one of the non-orbital tracks, and moving the area detector in synchronism therewith along the other non-orbital track;
a convolution unit for performing a convolution process on the projection data detected in the varied scan positions; and
a back projection unit for performing the image reconstruction to generate three-dimensional volume data of the region of interest by projecting the projection data convoluted by the convolution unit back to predetermined lattice points of a three-dimensional lattice virtually set to the region of interest of the object radiographed.
With this apparatus, the convolution unit performs a convolution process on the projection data detected in the varied scan positions, and the back projection unit performs an image reconstruction to generate three-dimensional volume data of the region of interest by projecting the projection data convoluted by the convolution unit back to predetermined lattice points of a three-dimensional lattice virtually set to the region of interest of the object radiographed. The apparatus does not use the conventional method in which two-dimensional sectional image data is generated by adding detection signals to superimpose, on a single plane, a plurality of projection images acquired by radiography from varied angles (i.e. projection images acquired from varied scan positions). Instead, an image reconstruction is carried out to generate three-dimensional volume data of the region of interest by projecting projection images acquired from varied scan positions back to predetermined lattice points of the three-dimensional lattice. Three-dimensional volume data of the region of interest may be generated without performing radiography a plurality of times. Thus, three-dimensional volume data of the region of interest of the object is generated quickly.
Preferably, the scanning device is arranged to move one of the radiation source and the area detector linearly in a first direction, and to move the other linearly in synchronism therewith in a second direction parallel and counter to the first direction, with the sectional planes to be imaged of the object placed in between. The back projection unit is arranged to project the projection data for the varied scan positions back to the predetermined lattice points of the three-dimensional lattice, coordinates of the projection data being corrected according to an angle formed between a virtual center axis of revolution extending substantially through the center of the region of interest of the object and perpendicular to the sectional planes to be imaged, and a straight line extending from the radiation source in each of the varied scan positions to the center of the area detector. Thus, even where the radiation source and area detector are moved linearly and in parallel to each other for scanning action, an image construction may be carried out directly on the projection data (original image data) with no need to modify, e.g. plane-shift, the projection data (original image data).
Preferably, the area detector is a flat panel detector or an image intensifier, which enables a prompt generation of a three-dimensional image of the region of interest of the object.